This section provides background information related to the present disclosure which is not necessarily prior art.
Friction clutches of the type stated are used in motor vehicles with selectable four-wheel drive, in which a drive torque can be fed to a second, selectable axle. The clutch, which is designed as a multi-plate clutch, can be actuated by means of an actuator, i.e. the drive torque can be applied and removed. DE 10 2010 033 865 A1 shows a drive system of this kind.
DE 20 2005 017 525 U1 describes a friction clutch comprising a multi-plate clutch and an actuation device. The actuation device comprises two actuator rings, between which balls run on ramp-shaped structures. When the actuator rings are rotated relative to one another, this actuation device has a closing effect, i.e. the plates are pressed together. The force of the actuation device acts on the multi-plate clutch via an axial bearing. To release the pressure, a spring system designed as a diaphragm spring assembly is provided.
In the released mode, when there is separation by means of the clutch, a residual torque is transmitted in the devices according to the prior art.
An improvement in the actuating dynamics of a multi-plate clutch is provided by DE 10 2008 021 418 A1. In particular, a stop device which limits the release travel is provided. The release travel of the clutch is set in accordance with the temperature.
The residual torque can also be reduced through the design of the plates. Examples of this are shown by US 2005/0224310 A1, U.S. Pat. No. 2,968,381, GB578289A, EP 1 128 081 A2 and U.S. Pat. No. 7,234,580 B2.
A multi-plate clutch with lubrication when required is disclosed by EP 1 445 506 A1. The supply of lubricant is controlled by means of a selector valve.
DE 101 24 583 A1 attempts to reduce the residual torque in a multi-plate clutch by means of a coupling device which couples at least some of the plates independently of the plate carrier.